Federal Signal's TELS Extension Ringer Device is a compact strobe light which is activated by the ringing signal of a telephone system. The TELS is specifically designed for use with an analog telephone. The ringing signal of 40–150VAC, 16–60Hz and local 120VAC power is all that is required to activate a TelCom signal.

The TelCom device is intended to be mounted on a vertical surface such as a rigid wall or post. TelCom has a three–conductor, six–foot, 120VAC power cord extending from the unit. Connecting the TelCom device to the telephone network is accomplished by running a modular telephone line cord (RJ11) to an existing jack or a duplex jack (customer supplied) into an existing modular jack. The TELS is designed with a durable zinc die–cast housing painted with gray powder coat enamel, and features an internal solid–state relay.

This visual signaling device features a three–dimensional triangular strobe light with the word "PHONE" on each visible surface. The strobe flashes when the telephone rings.